This invention relates to electric fuses having an elevated voltage rating, e.g. a rating of 2.8 to 23 Kv. It relates more specifically to fuses whose dimensions are drastically reduced as set forth below in more detail.
The invention solves the problem of providing all purpose fuses having extremely small dimensions, i.e. fuses capable of interrupting very small overloads requiring 1 hr to cause fusion of the fusible element or elements thereof (ANSI Standard C 37.40-2.2.2.2).
A solution to the problem of enabling fuses to interrupt the entire wide spectrum of currents which may occur is disclosed in my U.S. Pat. No. 3,810,062, May 7, 1974 for HIGH-VOLTAGE FUSE HAVING FULL RANGE CLEARING ABILITY. The solution shown in that patent has limitations. The fuses cannot be miniaturized to the required extent. The beads of melamine resin wth inorganic fillers are relatively bulky and expensive and it requires particular care to maintain equidistance between the turns of the windings of the fusible elements if they are carrying beads and if their number exceeds two.
In order to adapt fuses for the interruption of very small currents it is necessary to cause series miltibreaks in each of the fusible elements. Fuses wherein small currents are caused to be interrupted by series multibreaks in the fusible element, or elements thereof are disclosed in U.S. Pat. No. 3,735,317, 05/22/73 to P. C. Jacobs for ELECTRIC MULTIBREAK FORMING CARTRIDGE FUSE, and in my patent 3,969,694, 7/13/76 for ELECTRIC FUSE FOR ELEVATED CIRCUIT VOLTAGES CAPABLE OF INTERRUPTING SMALL OVERLOAD CURRENTS, and in other printed publications. These solutions require auxiliary circuitry for severing the fusible element, or elements, at several points and are, for this reason, not sufficiently cost-effective.
The present invention eliminates the drawbacks inherent in prior art solutions to the problem at hand.